Shader "Unlit/DepthPrepassTransparent"
{
    Properties
    {
        // This property is necessary to receive the texture from the main material
        _MainTex("Texture", 2D) = "white" {}
        // This property is necessary to receive the alpha cutoff value from the main material
        _Cutoff("Alpha Cutoff", Range(0.0, 1.0)) = 0.5
    }
    SubShader
    {
        // This pass is for the depth pre-pass.
        // It writes depth for transparent objects that need it.
        Tags { "RenderType" = "TransparentCutout" "RenderPipeline" = "UniversalPipeline" }

        Pass
        {
            // Use the "DepthOnly" LightMode for URP to identify this as a depth pass.
            Name "DepthOnly"
            Tags { "LightMode" = "DepthOnly" }

            // Write to the depth buffer
            ZWrite On
            // Do not write to any color channels
            ColorMask 0
            // Standard back-face culling
            Cull Back

            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            // Includes for URP core functionality
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"

            // Match the properties block
            TEXTURE2D(_MainTex);
            SAMPLER(sampler_MainTex);
            half _Cutoff;

            struct Attributes
            {
                float4 positionOS   : POSITION;
                float2 uv           : TEXCOORD0;
            };

            struct Varyings
            {
                float4 positionCS   : SV_POSITION;
                float2 uv           : TEXCOORD0;
            };

            Varyings vert(Attributes input)
            {
                Varyings output;
                // Standard vertex transformation
                output.positionCS = TransformObjectToHClip(input.positionOS.xyz);
                output.uv = input.uv;
                return output;
            }

            half4 frag(Varyings input) : SV_TARGET
            {
                // Sample the texture to get the alpha value
                half alpha = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, input.uv).a;
                
                // Perform alpha clipping. Discard the fragment if its alpha is below the cutoff.
                // This ensures the depth shape matches the visible shape.
                clip(alpha - _Cutoff);

                // We don't need to return a color as ColorMask is 0,
                // but the function must return something.
                return 0;
            }
            ENDHLSL
        }
    }
}